This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Passive Strain Sensor 10s are capable of recording strain without any data or power cable tether and can be manufactured and deployed for a fraction of the cost of alternative strain gauges. Commercially available strain gauges have significant limitations when used to monitor a marine structure.
The most common strain gauge uses piezo-electric circuits applied to the material in consideration. To support these circuits, the sensor requires power and data cables which pass changes in resistance through to an amplifier that, using a transfer function, provides the experienced strain. These sensors provide real time strain information and sample on the order of kilohertz. Other monitoring methods employ variations of this conventional piezo-electric strain gauge.
Application of energy harvesting techniques and wireless data transmission allows strain gauges to be deployed without a power or data cable. Both of these options have limitations. Energy harvesting techniques heavily rely on solar energy for implementation on civil structures. Many locations on structures and infrastructures do not, however, provide direct sunlight. There are strain gauges which claim to be operable solely using energy harvested from the structure they are monitoring through capturing the energy associated with strain. These sensors have been shown to be unreliable; if the material does not experience significant strain for an extended period of time the sensor will deplete its stored energy and cease to function.
Additionally, the complexity of these sensors makes them quite costly. Data transmission has been achieved using cellular networks and local wireless networks. Sensors have been deployed on marine structures with wireless data transmission using local networks; however, without strain energy harvesting, these sensors still require a power cable. In the case of marine applications, an additional wireless signal onboard a military vessel is unwelcome and it is difficult to justify wireless implementation of data transfer when a power cable will already be required at every monitoring location—considering it is possible to simply bundle the data and power cable with negligible additional volume. Thus, leading back to the conventional piezo-electric strain sensor as the most viable option, which requires a central amplifier, and power and data transmission cables. Conventional strain sensing systems require tens of thousands of dollars per sensor to implement on civil structures where the monitoring locations are easily accessible.
The alternative strain sensors provided herein can record the experienced strain without requiring a power or data cable, or energy harvesting technique. In some embodiments, these alternative strain sensors are capable of being 3D printed, laser cut, CNC'd, or manufactured using conventional techniques and thus can be manufactured for a fraction of the cost of all alternative sensing methods.
The sensors are capable of recording maximum strain from tensile and compressive loads and can be extended to do so in multiple directions, a limitation of all other available sensing options.
Conventional strain gauges provide a wealth of data that needs to be interpreted to yield relevant information to decision makers. Presently, structural health monitoring (SHM) researchers are swimming in a sea of data producing little information. This is largely because the strain gauges and other sensors provide data that needs to be condensed, stored, and analyzed by methods such as rain flow counting which removes time history indexing in order to make the large amount of data manageable and ultimately interpretable. Analyzing the plethora of data produced by strain sensors is tedious and much of the data is superfluous. Ultimately, using this data to produce relevant and accurate structural health information for decisions is difficult.
Research is being conducted using Bayesian networks (BN) and other modeling techniques to update design-stage engineering assumptions to more closely match the current condition of a structure. Information provided to the BN in the present model is minimal in comparison with many of the SHM updating schemes. The network is presently only updated with information observed from physical inspections such as fatigue crack initiation and permanent set and has shown promising updating power. Additional updating power can be achieved by providing the network with the stress experienced at relevant encoded fatigue-prone details. It is expected that the addition of this data imposed as evidence to the network would increase its prognosis accuracy for structural health and reliability. Extending a BN capable of accurate structural reliability prognosis to a decision support tool would be the next step. This could provide decision makers with accurate, structural health information necessary to make decisions related to the structure's safety and reliability.
In some embodiments, the sensor system of the present teachings can comprise an additional appendage or component can be used to record the maximum experienced strain. In some embodiments, multi-axial strain measurement can be obtained using the same device through additional lever systems. These embodiments, like the aforementioned embodiments, can record strain measurements as a standalone unit without requiring a power or data cable, or energy harvesting technique. Furthermore, the sensor can be fabricated using additive manufacturing techniques and thus can be made for a fraction of the cost of all alternative sensing methods.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.